Method for grinding tooth flanks of toothed gear wheels



Filed April 19, 1966 June 4,1968 A.G.HAI.-J SIEIRI 3,386,213

METHOD FOR GRINDING TOOTH FLANKS OF TOOTHED GEAR WHEELS 5 Sheets-Sheet 1 $115.; 4 I R N QSF 15 '2 F15 F 3 I I June 4 1968 A. G. HAUSER 3,386,213

METHOD FOR GRINDING TOOTH FLANKS 0F TOOTHED GEAR WHEELS Filed April 19, 1966 s Sheets-Sheet a June 19 8 A. G. HAUSER 3,386,213

METHOD FOR GRINDING TOOTH FLANKS OF TOOTHED GEAR WHEELS Filed April 19, 1966 3 Sheets-Sheet 5 Q1 2 Q3 Q Q5 United States Patent 3,386,213 METHOD FOR GRINDING TQOTH FLANKS 9F TOQTHED GEAR WHEELS Alwin G. Hauser, Winterthur, Switzerland, assignor to Maag Gear Wheel & Machine Company Limited, Zurich, Switzerland, a company of Switzerland Fiied Apr. 19, 1966, Ser. No. 543,732 Ciaims priority, application Germany, Apr. 23, 1965, M 64,990 7 Claims. (Cl. 51--287) This invention relates to a method for grinding the flanks of gear teeth with a dished grinding wheel having an endface with a slight hollow-tapered shape, that is to say, with a shallow internal taper on the side facing the tooth flank, so that in theory a point of the grinding wheel edge, formed by the face of the shallow internal taper and the face of the rim of the grinding wheel, generates the tooth flanks. In theory, only one point of the said grinding wheel edge determines the final shape of the tooth flank, but in practice it is a small zone of the edge, and the diameter of the grinding wheel is selected at a somewhat greater value with reference to the abovementioned theoretical point.

A method has become known under the name zerodegree grinding in which two dished grinding wheels machine the tooth flanks, one grinding wheel operating on the left-hand tooth flank and the other grinding wheel operating on the right-hand tooth flank, while the two grinding wheel axes are located at an angle of 0 in relation to each other, that is to say, they are located in parallel to each other, and the gear wheel to be ground rolls on its base circle.

In this known method, for reasons of prejudice and habit, and in analogy with grinding methods in which two grinding wheels represent a tooth to be generated and are inclined at the meshing angle, it has become common practice to grind away the grinding allowance of the tooth flank, layer by layer. At the same time, the grinding pressure in the grinding zone exerts an axial thrust on the relatively weak grinding wheel which is thus subjected to undesirable bending with detrimental elfects on the accuracy or grinding performance. There is also a relatively high rate of wear of the grinding edge which is responsible for the accuracy of the tooth flank.

The grinding method in accordance with the invention eliminates these disadvantages and at the same time increases the grinding performance without impairing the accuracy of the generated tooth flanks.

According to this invention, the method of grinding the tooth flank of a toothed gear wheel by means of a dished grinding wheel having that end face which faces the tooth flank tapered inwardly from the periphery of the grinding wheel to provide a shallow dish, and in which the tooth flank theoretically is ground by a point in the edge of the r grinding wheel formed by the junction of the face of said shallow dish and the face of the grinding Wheel rim, is characterised in that the grinding wheel is in-fed towards the tooth flank by an amount substantially equal to the full grinding allowance left on completion of cutting of the gear wheel, is reciprocated along the width of the tooth flank in the general direction of the toothed gear wheel axis, and is reciprocated between the tooth tip and the tooth root, so that the removal of the grinding allowance is carried out substantially by the face of the grinding wheel rim.

The main wear of the dished grinding wheel therefore takes plac on the cylindrical or tapered rim whose diameter is, however, of little significance for the accuracy of the tooth flanks. At the same time, the axial elastic deformation of the grinding wheels is practically zero, an

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important and advantageous feature for the accuracy of the ground flanks. It is also possible for the gauging interval for checking the grinding wheel edgewhich ensures the accuracy of the gear teethto be considerably increased, so that the rate of wear of the grinding wheel dressing diamond is reduced. Moreover, since in practice only the surface of the rim of the grinding wheel is subject to wear, it is only this surface that requires dressing. Wheel dressing may therefore take place within the so-' called main or active machining time. The unproductive down times are thus reduced because it was in this time that, previously, the circumferential and side surfaces of the grinding wheel had to be dressed.

A further advantage is due to the fact thatv at least a substantial part of the grinding allowance is machined away in one operation in the direction from the tooth tip to the tooth root, while the return motion in the direction from the tooth root to the tooth tip merely results in finishing of the tooth flank.

The method of the invention ensure that a relatively large number of grinding grit particles on the circumference of the grinding wheel, the majority of which are widely spaced, carry out the machining work, so that localised heat accumulations remain small and rapid heat dissipation or a favourable heat distribution is achieved.

In the accompanying drawings:

FIG. 1 is a cross-section of part of a grinding wheel and a tooth flank, illustrating a prior art grinding method;

FIG. 2 is an elevation, looking in the direction of the arrow A in FIG. 1;

FIG. 3 is a cross-section of part of a grinding wheel and part of a tooth flank, illustrating the method according to the present invention;

FIG. 4 is a diagram illustrating the force components indicated in FIG. 3 and acting on the grinding wheel;

FIG. 5 is a similar view to FIG. 3, but showing a modifled grinding wheel edge;

FIG. 6 is a diagram illustrating the force components indicated in FIG. 5 and acting on the grinding wheel;

FIG. 7 is an elevation of the tooth flank and the grinding wheel, looking generally in the direction of the arrow B in FIG. 3 and on a smaller scale, and illustrating a zigzag track of the grinding wheel on the tooth flank;

FIG. 8 is a similar view to FIG. 7, but illustrating a track formed by step-by-step movement of the grinding wheel along the tooth profile;

FIG. 9 is a perspective view showing the engagement of the grinding wheel on the tooth flank.

The tooth grinding method which has become known as zero-degree grinding (0:grinding) is illustrated in FIG. 1 which shows a cross-section through a dished grinding wheel (having the diameter d and through the tooth flank of a tooth 2 which is to be ground. The undercut 3, the partial allowance Art for partial grinding, as well as the total grinding allowance u which is removed with several part-grinding operations, are shown to an exaggerated large scale. The axis of the grinding wheel 1 is stationary and the gear wheel with the tooth 2 rolls along the point 4 of the dished grinding wheel, or the tooth flank moves, in the direction of the arrow 5, along the point 4 while the tooth profile is generated owing to the wheel rolling on the base circle. The point 4 is a point on the grinding wheel edge which is formed at the junction of the internally tapered face 1a which provides the shallow dishing of the grinding wheel and the face 1b of the rim of the grinding wheel 1. A frequently employed track of the grinding wheel point 4 on the tooth flank which is to be ground is shown in FIG. 2 in the form of a zigzag dot-dash line 8. It is particularly the zone 7, shown in FIG. 2, of the shallow internally tapered face 1a of the dished grinding wheel 1 which grinds away the material, because with the small feeds of the grinding wheel in the prior art methods there is a deformation of the dished grinding wheel which has a detrimental effect on the accuracy, and in particular in the grinding performance, and which may also necessitate running out grinding without applying a feed. As a result, the grinding stress of the internal taper (as a component in the axial plane of the grinding wheel) produces a grinding force R6, acting in the direction of the arrow, where this grinding force may act substantially in parallel to the grinding wheel axis and may be located in the centre of gravity of the zone 7.

The grinding method in accordance with the present invention is illustrated in FIGS. 3 to 9 by way of example.

FIG. 3 shows a greatly enlarged section through a dished grinding wheel 11 and the tooth flank of a tooth 2 which is to be ground. During the grinding operation the point 14 moves along the tooth profile of the tooth 2, the point 14 being a point on the circular and effective sharp edge of the grinding wheel formed by the face 11a of the shallow internal taper and the face 11b of the cylindrical rim of the dished grinding wheel 11. During the first and only grinding pass in the axial direction of the grinding wheel the rim face 11b of the wheel 11 engages the tooth 2 along the entire width 11 of the grinding allowance, the cutting forces F to P (as components in the plane through the grinding wheel axis) being required to move the grinding wheel in the direction of the arrow along the profile. The resultant force is R (FIG. 4) which is located in the aforementioned plane at right angles to the grinding wheel axis. Most of the grinding work is done by the rim face 11b of the wheel 11; the face 11a of the shallow internal taper removes practically no material from the tooth flank. The return motion of the wheel 11 in the direction of the tooth root to the tooth tip, that is, opposed to the arrow 15, merely causes finishing of the tooth flank.

Since, in practice, a grinding wheel having the diameter d will not have a theoretically accurately sharp edge, as assumed in FIG. 3, but will have a small radius p as indicated in FIG. 5, it will be necessary to provide the grinding wheel 21 with a slightly tapered or conical rim face 21b with a taper angle 'y instead of the cylindrical rim of the grinding wheel 11 in FIG. 3. The force components F to F will then occur in the axial plane of the wheel 21 over the width 11 of the grinding pass. These forces lead to a resultant force R (FIG. 6) which is located at right angles to the grinding wheel axis in the aforementioned plane. The wheel 21, with the decisive point 24, executes a movement in the direction of the arrow along the tooth profile.

To cover the entire tooth flank in the direction of the tooth Width b (FIGS. 7 and 8) and the tooth height or profile, it will be necessary to obtain relative motion between the grinding wheel and the tooth flank. It is advantageous if the movement of the grinding wheel takes place much more slowly in the profile, or tooth height, direction of the tooth (that is, from tooth tip to tooth root, and vice versa) than the movement of the grinding wheel in relation to the direction represented by the longtiudinal axis of the tooth (that is lengthwise of the width of the tooth). According to FIG. 7, the movement of the grinding wheel in the direction from the tooth tip to the tooth root, and vice verse, is assumed to be continuous and uniform and is superimposed to the more rapid reciprocating motion in the direction of the tooth width.b, the actual length b of the movement being somewhat greater than the tooth width b. The two components of motion therefore result in a zig-zag track, in accordance with the solid line in the direction from the tooth tip to the tooth root, and the broken line 31 in the direction from the tooth root to the tooth tip. The ratio of the two motions at right angles to each other is vzb v representing the grinding feed or the movement of the point 2-: along the tooth profile during or between successive passes of the point across the tooth width. If the motion of the grinding wheel along the tooth profile is a step-by-step motion, the point 24 follows 'a track of the shape shown in FIG. 8. The solid line 32 represents the motion of the wheel 21 from tooth tip to tooth root, the broken line 33 representing the motion in the direction from tooth root to tooth tip.

Normally, two grinding wheels take part in the machining process, one grinding wheel machining all lefthand tooth flanks and the other wheel machining all righthand' tooth flanks.

In order to maintain the cutting pressures practically constant during the active grinding process it is important to ensure that the relative motion between workpiece (the tooth) and the grinding wheel is made uniform in the direction of the tooth profile, that is between the tooth tip and the tooth root. This means that the grinding feeds v in the direction of the tooth profile will have constant values, if-as is normally the casethe grinding allowance u over the tooth profile and the tooth width b is constant. For a certain grinding wheel diameter d the are b (FIG. 9) along which the rim of the grinding wheel 11 effectively touches the workpiece will also be constant. In the event of uniform relative motion between grinding wheel and workpiece in the direction of the tooth width b, the amounts of material Q to Q which are ground away will also be identical to each other. In the method according to the present invention, a relatively large number of grinding grit particles therefore carry out machining work, the aforementioned grinding grit particles being widely spaced from each other if the grinding wheel is suitably selected for the purpose. This will minimize localised heat accumulations and ensure rapid heat dissipation or a favourable heat distribution.

The position of the grinding wheel edge plane (FIG. 3 point 14, also FIG. 5 point 24) in relation to the tangential plane of the radius of curvature of the affected profile section may be 0 but may also be some positive or negative angle.

What I claim and desire to secure by Letters Patent is:

1. The method of grinding the tooth flank of a toothed gear wheel by means of a dished grinding wheel having that end face which faces the tooth flank tapered inwardly from the periphery of the grinding wheel to provide a shallow dish, and in which the tooth flank theoretically is ground by a point in the edge of the grinding Wheel formed by the junction of the face of said shallow dish and the face of the grinding wheel rim, characterised in that the grinding wheel is in-fed towards the tooth flank by an amount substantially equal to the full grinding allowance left on completion of cutting of the gear wheel, is reciprocated along the width of the tooth flank in the general direction of the toothed gear wheel axis, and is reciprocated between the tooth tip and the tooth root, so that the removal of the grinding allowance is carried out substantially by the face of the grinding wheel rim.

2. The method according to claim 1, characterised in that the motion of the grinding wheel in the profile direction of the tooth takes place more slowly than the motion of the grinding wheel in the direction of the axis of the toothed gear wheel.

3. The method according to claim 2, characterised in that a reciprocating motion of the grinding wheel in the direction of the tooth trace of the gear wheel is superimposed on a uniform motion along the tooth profile in the direction between the tooth tip and the tooth root, so that a sig-zag machining track is produced.

4. The method according to claim 2, characterised in that the motion of the grinding wheel along the tooth profile in the direction between the tooth tip and the tooth root is carrier out in steps during the reciprocating motion in the direction of the tooth trace of the gear wheel so that a stepped machining track is produced.

5. The method according to claim 4, characterised in that the steps for generating the tooth profile are selected 5 to be of identical magnitude in relation to the tooth profile so that the material removed by the grinding wheel, and therefore the cutting pressures which occur during the active grinding process of one flank, remain practically constant.

6. The method according to claim 1, characterised in that the effective grinding edge of the grinding wheel at the rim thereof is provided with a profile such that when the feed towards the tooth flank is substantially equal to the full grinding allowance, the resultant of the grinding forces is located substantially at right angles to the granding wheel axis.

7. The method according to claim 6, characterised in that, the effective grinding wheel edge being radiused, the surface of the rim is the surface of a truncated cone Whose major diameter is adjacent the said effective edge.

References Cited UNITED STATES PATENTS 1,642,708 9/ 1927 Wirrer 5 1-5 6 1,773,677 8/ 1930 Herrmann 5156 1,964,233 6/ 1934 Uhlich 51--287 LESTER M. SWINGLE, Primary Examiner. 

1. THE METHOD OF GRINDING THE TOOTH FLANK OF A TOOTHED GEAR WHEEL BY MEANS OF A DISHED GRINDING WHEEL HAVING THAT END FACE WHICH FACES THE TOOTH FLANK TAPERED INWARDLY FROM THE PERIPHERY OF THE GRINDING WHEEL TO PROVIDE A SHALLOW DISH, AND IN WHICH THE TOOTH FLANK THEORETICALLY IS GROUND BY A POINT IN THE EDGE OF THE GRINDING WHEEL FORMED BY THE JUNCTION OF THE FACE OF SAID SHALLOW DISH AND THE FACE OF THE GRINDING WHEEL RIM, CHARACTERISED IN THAT THE GRINDING WHEEL IS IN-FED TOWARDS THE TOOTH FLANK 